This invention relates to the modification of a water-soluble acrylic polymer, and more particularly to a process for modifying a water-soluble acrylic polymer to form a water-soluble modified product.
Polyacrylamide which is a water-soluble high polymer serves in many commercial fields as a flocculant, a thickener, a chemical agent for paper manufacture, etc.
Various modified polymer of polyacrylamide, that is, polyacrylamide derivatives, carbamoyl groups of which are partially substituted with other substituents, also have a wide range of application as well as polyacrylamide.
The modification of polyacrylamide is generally carried out by adding a reagent required for the modification to an aqueous solution of the polymer. This method, however, is only applicable when the concentration of polymer in the solution is less than about 20%, because an increase in the concentration makes the polymer solution considerably viscous and the viscous solution is handled with difficulty. As a result of this, a large amount of water should be removed in order to obtain a modified polyacrylamide product in a solid form. If the modified polyacrylamide product is served for commercial use without the removal of water, thus in the solution form, it is very inconvenient for handling and transporting.
There is disclosed in German Patent Specification No. 1,220,610 a method for overcoming the above-described drawbacks, in which method a polymer is made contact with a particular reagent in the mixture small amount of water and an organic solvent which does not dissolve the initially charged polymer nor the modified product thereof and is insoluble in water. Since it is desired to carry out the reaction uniformly, the polymer should be in the form of possible finest particle so that the polymer has a larger contacting surface area. However, when the size of polymer particles is smaller, during the swelling of the polymer with the reagent the moisture content in the surface portions of polymer particles increases. Thus the adhesiveness of particles increases so that the particles adhere to each other to form a mass, resulting in a nonuniform reaction. This shows that there is a certain limit on the size of polymer particles. Furthermore, it is not preferable from the safety maintenance viewpoint to use a large amount of the organic solvent which is combustible.